The present invention relates to heat sinks in general, and more particularly to heat sinks for use in dissipating waste heat generated by electrical or electronic components and assemblies.
Research activities have focused on developing heat sinks to efficiently dissipate heat from highly concentrated heat sources such as microprocessors and computer chips. These heat sources typically have power densities in the range of about 5 to 35 W/cm2 (4 to 31 Btu/ft2s) and relatively small available space for placement of fans, heat exchangers, heat sinks and the like.
At the component level, various types of heat exchangers and heat sinks have been used that apply natural or forced convection or other cooling methods. The most commonly existing heat sinks for microelectronics cooling have generally used air to directly remove heat from the heat source. However, air has a relatively low heat capacity. Such heat sinks are suitable for removing heat from relatively low power heat sources with power density in the range of 5 to 15 W/cm2 (4 to 13 Btu/ft2s). Increases in computing speed resulted in corresponding increases in the power density of the heat sources in the order of 20 to 35 W/cm2 (18 to 31 Btu/ft2s) thus requiring more effective heat sinks. Liquid-cooled heat sinks employing high heat capacity fluids like water and water-glycol solutions are more particularly suited to remove heat from these types of high power density heat sources. One type of liquid cooled heat sink circulates the cooling liquid so that the liquid removes heat from the heat source and is then transferred to a remote location where the heat is easily dissipated into a flowing air stream with the use of a liquid-to-air heat exchanger. These types of heat sinks are characterized as indirect heat sinks.
As computing speeds continue to increase even more dramatically, the corresponding powers densities of the devices rise up to 100 W/cm2. The constraints of the necessary cooling system miniaturization coupled with high heat flux calls for extremely efficient, compact, simple and reliable heat sinks such as a thermosiphon. A typical thermosiphon absorbs the heat generated by the electronic device by vaporizing the captive working fluid on a boiling surface of the heat sink. This process is governed by well-known general theories of nucleate boiling. The vapor is then transferred to an air-cooled condenser where it liquefies by the process of film condensation over the condensing surface of the thermosiphon. The heat is rejected into an air stream flowing over a finned external surface of the condenser. The condensed liquid is returned back to the boiler by gravity. The heat transfer rate from the air-cooled fins on the exterior of the condenser is much lower than that for the processes of boiling and condensing occurring inside the thermosiphon. Therefore the corresponding fin area is necessarily relatively large compared to the chip surface area generating the heat.
The compact thermosiphons intended to fit in a computer case require boiling and condensing processes to occur in close proximity to each other thereby imposing conflicting thermal conditions in a relatively small volume. This poses significant challenges to the process of optimizing the thermosiphon performance.
Thus, what is desired is a thermosiphon optimization process to intensify the processes of boiling, condensation and convective heat transfer at the external surface of the condenser while maintaining low airside pressure drop.
One aspect of the present invention is a thermosiphon for cooling an electronic device having a mean width of dimension xe2x80x9cbxe2x80x9d. The thermosiphon comprises a boilerplate having a top surface and including a plurality of pyramid shaped fins projecting upwardly from the top surface. The boilerplate also has a bottom surface for receiving the electronic device to be cooled. A plurality of spaced apart condenser tubes is mounted above the boilerplate such that the boilerplate and the condenser tubes define a vapor chamber therebetween for receiving a working fluid therein. A plurality of convoluted fins extends between each adjacent pair of condenser tubes.
Another aspect of the present invention is a thermosiphon for cooling an electronic device having a mean width of dimension xe2x80x9cbxe2x80x9d. The thermosiphon comprises a boilerplate having a top surface including a plurality of pyramid shaped fins projecting upwardly from the top surface and a bottom surface for receiving the electronic device to be cooled. A plurality of spaced apart condenser tubes is mounted above the boilerplate. Each condenser tube has opposing side walls and at least one transverse partition wall extending between the opposing side walls and is intermediate the ends of the condenser tube. The boilerplate and the condenser tubes define a vapor chamber therebetween for receiving a working fluid therein. A plurality of convoluted fins extends between each adjacent pair of the condenser tubes.
Yet another aspect of the present invention is a heat sink assembly for cooling an electronic device. The heat sink assembly comprises an air moving device housed in a shroud for causing an axially directed airflow through the shroud and a duct having one end thereof attached to the shroud and in fluid communication therewith. And a thermosiphon attached to a second end of the duct and in fluid communication therewith. The thermosiphon comprises a boilerplate having a top surface and including a plurality of pyramid shaped fins projecting upwardly from the top surface. The boilerplate also has a bottom surface for receiving the electronic device to be cooled. A plurality of spaced apart condenser tubes is mounted above the boilerplate such that the boilerplate and the condenser tubes define a vapor chamber therebetween for receiving a working fluid therein. A plurality of convoluted fins extends between each adjacent pair of condenser tubes.
These and other advantages of the invention will be further understood and appreciated by those skilled in the art by reference to the following written specification, claims and appended drawings.
FIG. 1 is a perspective view of a thermosiphon and cooling fan embodying the present invention, wherein the fan is arranged to force cooling air through the thermosiphon.
FIG. 2 is an elevational cross-section view of the thermosiphon shown in FIG. 1 and taken along the line 2xe2x80x942.
FIG. 3 is a partially broken perspective view of a condenser tube utilized in the thermosiphon of FIG. 1.
FIG. 4 is an enlarged perspective view of the pyramid fin array formed on the boilerplate.
FIG. 5 is a enlarged perspective view of a non-uniform array of pyramid fins on the boilerplate.
FIG. 6 is an enlarged elevation view of one of the pyramids from the array illustrated in FIG. 4.
FIG. 7 is an alternate embodiment of a thermosiphon cooling assembly utilizing two cooling fans.